This pioneering work reports successful androgenic plant development via embryogenesis from microspore calluses in anther cultures and estimation of bioactive metabolites in in vitro regenerants and parent plant (control) of Cambod tea, Camellia assamica ssp. lasiocalyx (Planch MS) cultivar TV19. Anthers bearing microspores at early-to-late uni-nucleate stage were selected to initiate androgenesis. A pre-treatment of 5 0 C for ve days in the dark was most effective to initiate profusely growing white callusing from microspores within 10 weeks of culture on MS medium (6% sucrose) supplemented with high cytokinins/ auxin ratio maintained by benzyl adenine (BAP) and 2,4-dichlorophenxyacetic acid (2, 4-D). Nodular structures on the callus surface differentiated into embryos. Further developement of the embryos occurred on embryogenesis medium but, with ten times reduced concentration of growth regulators and additives. Germination of embryos into complete plantlets was achieved when major salts in medium were reduced to half MS (½ MS) and augmented with BAP, GA 3 and IBA along with glutamine and serine. Cytological examination of the root-tip cells revealed that regenerated plantlets were haploids (2n=x=15), which was further con rmed through ow cytometry. The hot-water extracts from in vitro haploid calluses, embryos and eld-grown donor plant were utilized for quanti cation of (+)-catechin, (-)-epicatechin, (-)-epigallocatechin gallate, caffeine and theophylline. Our ndings revealed that the metabolite pro le of in vitro regenerated haploid cultures is comparable to that of the mother plant, thereby presenting them as potential source for genome duplication and development of genetically stable homozygous pure breeding lines.
Key MessageThis is rst report on haploids in out-breeding tree, Cambod tea. Its a signi cant achievement towards generating homozygous lines, which is impossible using conventional methods. Haploids showed consistent metabolite production.
Post flowering stalk rot (PFSR) of maize caused by the Fusarium species complex is a serious threat to maize production worldwide. The identification of Fusarium species causing PFSR based on morphology traditionally relies on a small set of phenomic characteristics with only minor morphological variations among distinct Fusarium species. Seventy-one isolates were collected from 40 sites in five agro-climatic zones of India to assess the diversity of Fusarium spp. associated with maize crops showing symptoms of PFSR in the field. To investigate the pathogenicity of Fusarium spp. causing PFSR sixty isolates were toothpick inoculated between the first and second node at 55 days after sowing during the tassel formation stage of the crop in Kharif (Rainy season), and Rabi (Winter season) season field trials. Ten most virulent Fusarium isolates, based on the highest observed disease index, were identified by homology and phylogenetic analyses of partial sequences of the translation elongation factor 1 α (Tef-1α). Based on morphological traits such as mycelial growth patterns and mycelial pigmentation, Fusarium isolates were divided into nine clusters. The isolates were judged to be virulent based on their ability to decrease seedling vigour in in-vivo situations and high disease severity in field experiments. Pathogenicity test during the Kharif season showed 12 isolates with virulent disease symptoms with a mean severity ranging between 50 to 67 percent disease index (PDI) whereas in Rabi season, only five isolates were considered virulent, and the mean severity ranged between 52 to 67 PDI. Based on pathological characterization and molecular identification, 10 strains of Fusarium species namely, Fusarium acutatum (2/10), Fusarium verticillioides (Syn. Gibberella fujikuroi var. moniliformis) (7/10), Fusarium andiyazi (2/10) recorded the highest diseases index. All these species are part of the Fusarium fujikuroi species complex (FFSC). The distribution of virulent isolates is specific to a geographical location with a hot humid climate. Increased knowledge regarding the variability of Fusarium spp. responsible for PFSR of maize occurring across wide geographical locations of India will enable more informed decisions to be made to support the management of the disease, including screening for resistance in maize-inbred lines.
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